patch 8.2.2173: Vim9: get internal error when assigning to undefined variable

Problem:    Vim9: get internal error when assigning to undefined variable.
Solution:   Add error message. (closes #7475)
diff --git a/src/version.c b/src/version.c
index f374d43..1a45c95 100644
--- a/src/version.c
+++ b/src/version.c
@@ -751,6 +751,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    2173,
+/**/
     2172,
 /**/
     2171,